1. Field of the Invention
The present invention relates to a method of controlling an exhaust gas purification system and an exhaust gas purification system, wherein an exhaust gas temperature raising control is conducted accompanying in-cylinder multi-injection, in order to recover the purification ability of a diesel particulate filter device for purifying components in the exhaust gas of an internal combustion engine such as a diesel engine.
2. Description of the Related Art
Regulations are becoming stricter every year regarding the emission quantities of particulate matter (hereinafter referred to as PM) such as NOx, CO, and HC exhausted from diesel engines. Technology is being developed to reduce the quantities of PM exhausted outside the engine, wherein such PM is trapped by a filter referred to as a diesel particulate filter (hereinafter referred to as DPF). Among such technologies, there exists a catalyst-supporting, continuous regeneration-type DPF device.
In this continuous-regeneration-type DPF device, when the exhaust gas temperature is at or above 350° C., PM trapped at the filter is continuously purified by combustion, and the filter is self-regenerating. However, when the exhaust temperature is low, for example during a sustained, low exhaust gas temperature state such as when the internal combustion engine is idling or operating with low load or at low speeds, the low exhaust gas temperature lowers the catalyst temperature, and thus the catalyst becomes inactive. For this reason, oxidation reactions are not promoted, and it becomes difficult to regenerate the filter by oxidizing PM. Consequently, PM accumulation at the filter becomes prolonged and the filter becomes increasingly plugged, thereby resulting in the problem of the exhaust pressure rise due to filter plugging.
One technique for solving such problems involves conducting a regeneration control, wherein the temperature of the exhaust gas is forcibly raised when filter plugging exceeds a predefined amount, and trapped PM is forcibly removed by combustion. In this regeneration control, an exhaust gas temperature raising control is conducted to raise the temperature of exhaust gas flowing into the filter to a temperature equal to or greater than the temperature at which PM trapped at the filter burns. In so doing, the filter is forcibly regenerated by increasing the filter temperature to remove PM by combustion.
A method for conducting such an exhaust gas temperature raising control exists, wherein multi-injection (multi-stage delayed injection) or post-injection is conducted as part of in-cylinder fuel injection. Multi-injection is a delayed multi-stage injection, wherein fuel is injected in-cylinder over multiple stages. With multi-injection, the quantity of burned fuel inside the cylinder is increased without additional work, and the temperature of the exhaust gas exhausted from the cylinder is increased. In other words, the temperature of exhaust gas flowing into the oxidation catalyst device can be raised to a temperature equal to or greater than the catalytic activation temperature of the oxidation catalyst.
In addition, post-injection is an injection conducted during in-cylinder injection as an auxiliary injection, occurring after the primary injection at a timing later than that of the multi-injection. With post-injection, the amount of HC (hydrocarbons) is increased in the exhaust gas exhausted from the cylinder. By oxidizing the HC with an oxidation catalyst, the temperature of exhaust gas downstream to the oxidation catalyst device can be increased.
However, there is also the problem of oil dilution occurring when unburned fuel due to post-injection is mixed with the engine oil (lubricating oil). In order to counteract this problem, a control is performed such that forced regeneration is conducted when the vehicle is stopped and idling and operating conditions are stable. In this control, when a predefined quantity of PM has accumulated at the filter device, the driver is notified that regeneration control of the filter device is necessary, using warning means such as a warning lamp or similar indicator. Upon receiving this notification, the driver stops the vehicle, and by pressing a manual regeneration button, the vehicle enters manual regeneration mode and conducts forced regeneration.
In the system, an oxidation catalyst device is installed anterior (upstream) to the filter device. By using this oxidation catalyst device to oxidize HC supplied to the exhaust gas by post-injection, the temperature of exhaust gas at the filter device inlet is raised, and forced regeneration is executed.
For example, as disclosed in Japanese Patent Application Kokai Publication No. 2004-225579 and Japanese Patent Application Kohyou Publication (Translation of PCT Application) No. 2002-066813, exhaust temperature raising controls involve the following. When the exhaust gas temperature is low, such as when the engine is in a low-speed or low-load operational state, a first exhaust gas temperature raising control is conducted, wherein the first in-cylinder fuel injection control involves conducting multi-injection without post-injection. In so doing, the temperature of the oxidation catalyst device is raised to a temperature equal to or greater than the catalytic activation temperature of the oxidation catalyst. Subsequently, after having raised the oxidation catalyst device to a temperature equal to or greater than the catalytic activation temperature, post-injection is conducted in addition to multi-injection while the exhaust gas is maintained at a temperature equal to or greater than the catalytic activation temperature as part of a second exhaust gas temperature raising control wherein post-injection is conducted as part of the in-cylinder fuel injection control. In so doing, HC is supplied to the oxidation catalyst device. Since HC generates heat when oxidized by the oxidation catalyst, the exhaust gas flows into the filter device in a state of even greater temperature. Subsequently, when this high-temperature exhaust gas causes the filter device to meet or exceed the temperature at which PM starts to burn, accumulated PM is removed by combustion. At this point, a temperature maintenance control is conducted wherein multi-injections are continued in order to keep the exhaust temperature equal to or greater than the activation temperature of the oxidation catalyst, but wherein post-injections are not conducted.
In the first exhaust gas temperature raising control, the second exhaust gas temperature raising control, as well as the temperature maintenance control, the injection quantities and injection timings of the multi-injections are controlled on the basis of map data, the map data being based on engine revolutions and fuel injection quantities. This map data is configured in advance by experiment, calculation, or similar methods.
However, in the related art, control is conducted using the same map data for the first exhaust gas temperature raising control, the second exhaust gas temperature raising control, as well as the temperature maintenance control. For this reason, it is difficult to achieve both temperature raising performance and temperature maintenance performance. Consequently, there have been problems in that the time for the temperature raising becomes longer and fuel consumption worsens.
Patent Literature 1: Japanese Patent Application Kokai Publication No. 2004-225579
Patent Literature 2: Japanese Patent Application Kohyou Publication (Translation of PCT Application) No. 2002-066813